Recovery of a diolefin with liquid methane



Aug- 2, 1966 w. c. MCCARTHY ETAL 3,264,363

RECOVERY OF A DIOLEFIN WITH LIQUID METHANE Filed Nov. 16, 1964 2Sheets-Sheet 1 Allg. 2, 1966 w. c. MCCARTHY ETA| 3,264,363

RECOVERY OF A DIOLEFIN WITH LIQUID METHANE A T TORNEYS United StatesPatent O 3,264,363 RECOVERY F A DILEFIN WTH LIQUID METHANE William C.McCarthy and Glenn H. Bale, Bartlesvilie,

0kla., assignors to Phillips Petroleum Company, a corporation ofDelaware Filed Nov. 16, 1964, Ser. No. 411,467 Claims. (Cl. 26d-681.5)

This invention relates to the recovery of `a diolefin from an admixtureof the dioleiin with an olefin utilizing liquid methane as a selectivesolvent. In one aspect the invention relates to the use of liquidmethane under extracting conditions to recover isoprene from adehydrogenation effluent. In another aspect the invention relates to therecovery of isoprene from an admixture of isoprene With at least onemonooleiin from which it is ordinarily difficult to separate.

Dioleiins may be produced by many different methods, one `of the mostcommon being the cracking or dehydrogenation of petroleum oils andgases. In many such methods, the diolefins are found in an impure state,being admixed with hydrogen and with monoolefins and/or parafiins ofvarious boiling points, as the chief impurities. For most chemicalprocesses in which diolens are used commercially, it is desirable tohave a relatively high concentration of dioleiins available and this isespecially true when the dioleiins are to be used to form rubber-likepolymers, a purity Iof 95 percent or better being sometimes required forthis purpose. While the hydrogen and the hydrocarbons having boilingpoints considerably different from the -diolens being purified may beremoved easily by fractional distillation, it is very diiiicult toseparate the diolefins from those hydrocarbons having boiling pointsclose to the diolefins, since very efiicient fractionation is required,yand this is not commercially feasible in most cases, particularly whenazeotropes are formed by the dioleiins and impurities.

Because of the ditiiculty of obtaining substantially pure dioleiins bydistillation methods alone, solvent extraction has been utilized in anattempt to separate dioleiins in a high state of purity from hydrocarbonmixtures. While it is comparatively easy to make such a separation fromparan hydrocarbons, it has been found that the separation frommonooleiins is more difficult because many solvents which are selectivefor diolens have a considerable aiiinity for monooleiins also.Accordingly, it has become desirable to find a solvent which willselectively separate diolefins from monooleiins.

It has now been discovered that liquid methane can be utilized as aselective solvent to separate a diolen from a monoolefin. In oneembodiment a stream containing isoprene and monoolens with at least 72weight percent isoprene can be contacted with a liquid methane stream tolsubstantially increase the isoprene concentration in the raffinatestream. In another embodiment of the invention a stream containingisoprene and monooleiins is contacted in a liquid-liquid extraction zonewith an upwardly flowing stream of liquid methane and a downwardlyflowing stream of a secondary solvent to provide a product concentratedin isoprene.

It is an object of the invention to provide a novel method for therecovery of a dioleiin from a mixture of the dioleiin with monooleiins.It is an object of the invention to provide a novel and improved methodof concentrating an isoprene stream. A further object of the inventionis to provide a process for obtaining a high purity diolen stream in acommercially practicable manner. Another object of the invention is toprovide a novel and improved method for the recovery of isoprene from amixture of hydrocarbons, for example the effluent from a dehydrogenationreaction. It is another object of the Patented August 2, 1966 'iceinvention to provide a combination of steps for the recovery of isoprenein a technically and economically feasible manner.

Other aspects7 objects .and advantages of the invention Will be apparentfrom a study of the disclosure, the drawings and the appended claims.

In the drawings FIGURE 1 is a schematic representation of a process inaccordance with a first embodiment of the invention for recovering astream having a high concentration of isoprene, and FIGURE 2 is aschematic representation of a process in accordance with a secondembodiment of the invention for recovering isoprene utilizing dualsolvents.

While the invention is broadly applicable to the separation of adioleiin from a mixture of the dioleiin with a monooleiin, for sake ofsimplicity the invention will be described in terms of the separation ofisoprene from the eluent of a two-stage process for the dehydrogenationof isopentane, The purification of isoprene from this effluent isdifficult to effect by ordinary fractional distillation. This isevidenced by the following table showing the boiling points of theprincipal components of the C5 fraction of the isopentanedehydrogenation eflluent and their relative volatility compared toisoprene:

Zmethylbutene From the order of boiling points, it will be seen that toaccomplish the desired separations by ordinary fractional distillation,the C5 fraction has to be resolved into its individual components. Thethree amylenes would have to be recombined for recycle to the seconddehydrogenation stage. Because of the small spread in boiling points,good separations by fractional distillation require a large number oftrays. Therefore, extremely expensive fractionation equipment is neededin order to effect the separation of individual constituents.Furthermore, if a fractional distillation is made upon the efliuent ofthe twostage isopentane dehydrogenation at extremely high reflux ratiosto obtain very narrow fractions, prolonged heating of the mixtures isinvolved; and as a result, considerable polymerization of the moreunsaturated compounds commonly occurs. Thus, fractional distillationalone as a means for separating very narrow fractions from such mixturesis disadvantageous. Complex mixtures such as above tabulated can beadvantageously resolved into their individual constituents by a processin accordance with the present invention.

Referring now to the drawing, and to FIGURE 1 in particular, isopentaneis passed by way of pipe 2 into dehydrogenation zone 3 wherein there isproduced an efliuent stream containing isopentane, the methyl butenesand isoprene. This stream is passed by way of pipe 4 to fractionator 5from which there is removed as overhead by way of pipe 6 C4 and lighterhydrocarbons. There is obtained from fractionator 5, as a side stream, a`stream consisting essentially of isopentane, methyl butenes, landisoprene. This side stream is passed by way of pipe 7 to la iirstsolvent extraction zone or column 8. Heavier materials from lthefractionator 5 are removed as a bottoms stream through pipe 9. In thesolventextraction zone 8, there is formed a raffinate phase containingessentially isopentane which is recovered .and recycled by way of pipeto dehydrogenation zone3. Extract phase is passed by way of pipe 11 andvalve 12.

to solvent stripperl zone 13 from which recovered solvent is removed:and recycled by lway of pipe 14 and pump 15, and extract material,consisting essentially of methyl butenes and isoprene, .is removed byway of pipe- 16 and pump 17. A portion ofr the material in pipe 16 ispassed through pipe 18 into a lower portion of zone 8 as reu'xV whilethe remainder is passed through pipe 19 to a second solvent extractionzone 21.5.. In `solvent-extraction zone:

21, therel is formed a raiiinateV phase from which methyl butenes arerecovered and recycled by way of pipes160' and22 to dehydrogenation zone24. Steam is introduced Vinto zone 24 by'way of pipe. 23. IIn'zone124,further.

quantities of isoprene are produced by dehydrogenation of thek methylbutenestream, the effluent being. passed by .Y

w-ay of pipe 25 to phase separator'26-wherein' water is separated andremoved through pipe 27. The hydrocarbons are .passed through pipe 2S topipe 4 for treatment together with the isopentane-dehydrogenationzoneeuent as already described above. The extract from'solventextractionzone 21which contains isoprene is passed-by way of pipe V31 and valve 32.to solvent'strip'per .33'from which recoveredsolvent is recycled-.toz-one 21 by .way

of pipe 34`and pump 35. The extract material, containing at least 72weight percent isoprene with the .remainder beingk primarily-methylbutenes, is Withdrawnffrom solvent stripping zone 33 by way of pipe 36rand-pump 37..Iv

A portion ofthe materialin pipe 36 is passed through pipe 39 intoliquid-liquidextractionzone 41.1 Solvents:

which can be used in extraction zones 8 lands-21 include furfural,methylf'carbitol, acetonitrile, ethylene: glycol, the glycol ethers,etc.

:'30 pipe 38 vto a llower Yportron ofl1qu1d-l1quid extraction 2 zone 21as redux while the remainder is passed through I In accordance Withtheinvention; liquid methane, is introduced by way of pipe-42intoaa lowerportio'noffy liquid-liquid extraction column-41. Column 41 Sis'oper-:ated at `suitable temperature and pressure to maintain` fthe methane inthe liquid phase within column 41.:V The extract stream consistingprimarily of methyl butenes and liquid .methane iis passed through`pipe-43 containing .a

pressure reduction valve 44 into solvent stripper 45.2` The methane isvaporized upon passing `through valve.

44. The vgaseous methane is lWithdrawn from stripper` 45 and passed byway of pipe 46 to the inlet of compressor 47. The compressed methane ispassed through :pipe

48 and condenser 49 to liquefy the methane. The Vthus liqueed methaneis'returned to column 41 through vpipe- 42. The methyl butenes arewithdrawn from separator 45 by way of pipe 51 and pump 52. A portion ofthe thus withdrawn methyl butenes c-an be returned through pipe 53 to anupper portion of column 41 as reflux while the remainder is passedthrough pipes 54 and 22 to olen dehydrogenation zone 24. A high purityisoprene product stream containing some dissolved methane is with-fdrawn from ythe lower portion of column 41 by way.r of

pipe 55 and passed through pressure reduction valve 56a into ash vessel57 'from which gaseous methane is recycled through pipe 58 .to pipe 46.High purity isoprene free ofmethane is removed through pipe 59.

The utilization of a solvent selective for the minor component ratherthan the major component permits a substantial reduction in the amountvof solvent required. Thus the requirements for liquid methane, which'isser-,i lective for the monoolefms, the minor component,f in

liquid-liquid extraction zone 41 are considerably less than l.

nentr of 10 to l. Similarly the. use offa conventional solvent inextraction zone 21. to extract-the isoprene fraction, which is generallythe `minor component in zone`21l providesfor -a minimum requirementofsolvent.Y Thus the. f combination of a conventionaly solvent.selectivefor the.V

diolen in zoneI 21V and liquid methane, which is selective for themonooleiin, in zone 41 minimizes the overallsolventrequirements,providing a more complete. separation with favorable?economies.

Referring now to FIGUREZ there is. illustrated a sec. ond embodimentofthe inventioniwith :those elements` common lto FIGUREI .beingdesignatedbythe same numerals. The; hydrocarbonV stream comprising primarily'isoprene andmethyl butene ,passing through pipe v19 .is introducedintodual liquid-liquidextraction,column 61. -Liquid methane isi introducedinto a Alower portion of column 61 by way ofr pipe .62 whileV a dualsolvent is lintroduced into. an uppergportionof `column 61 by` way ofpipef 63.E Column 61 is operated at a temperature and; pressure toVmaintain `the methane in the liquid phases The dual solvent is;immiscible withliquid methane and thereby establishes two liquidI phasesin' theextractor regardless of the .concentration .of isoprene-inthe'`feedstream. This permits recovery of` high-purity visoprene from afeedstream :containing low concentrations. ofv said isoprene.` A.morexeicient separation is; Ialso obtained.

because liquid methane is selective for monoolens whereas the dualsolvent is` selective fo'rrisoprene;

Examples-of solventszsuitahle for use as the dual solvent Eincludealcoholsv such as, methyl. alcohol, 'ethyl alcohol,

and the like,; acetone-paraflinic hydrocarbons such as.

heptane, decane. and the like, aromatics such. asitoluene,

benzene, fand the like, .and cycloparain's such as methylcyclopentane,etc.k and mixtures'.threreot.I Anyrsolvent e YVselective l.for diolens'immiscible with. liquidf methane,

andhaving a very lowv freezing point willV suicle.;

The dual solvent passes downwardly .through column 61 selectivelyabsorbing;the `isoprene .while .the ,liquid methane passes-.upwardlyselcctivelyfV absorbing the-methyl butenes. ,The methanestream richy inmethyl butenes is f withdrawn fromcolumn 61 and ppassedby. way. of pipe-V 64 and valve 65 into solvent flash vessel 66 wherein the. f methaneis vaporized due ,tothe dropinV pressure across,V

Valve 65.: ,The methyl. butenes containing gsome'methyl" alcohol `arepassed by way of pipe 80.into solvent stripper 85.1from which butenes`are Withdrawn :and passediby way of pipe 67,ipump 68; and pipe 221into-olefin dehydroA genation zone 24. Alcoholis recycled via pipe y6?.The 1 gaseous methane. is kWithdrawn from ystripper 66 ytand passed hyway; of pipe 69 to the inlet of compressor 70.v

The compressed methane is passed through pipe: 71 yinto condenser72'jwherein the methane is liquefied.; The.4

liquefied methane isf-returned to column;61 by way of pipe 62. The dualsolvent stream rich in isoprene .and

containing some methane is lwithdrawnfrom .column 61 v and passed byway. of pipe 75 and reducing valve 76' into ash tank 77 tovaporize 4themethane.. The gaseous@ methane is passed fromrfla'sh tank 77 .throughpipe 78 to the inlet of compressor 70.' The .dual solventcontainingisoprene is then passed `throughl pipe ,79 into fracf.

tionator 811 The isoprenezis withdrawn from fractionator 81 by way ofpipe .82 and passed to =a pointof storage or utility as desired. Thedual solvent'is withdrawnv from.

fractionator 81 and returned 5to the upper portion yof column61wbyway ofpipe .83, pump 84 and pipe-63n If desired, isoamylenes obtainedbysulfuric acidextraction of catalytically cracked gasoline can beydehydrogenated .rather than .isopentane yunit 24 and unit I3 is notrequired. Extractor 8 is not required, the efliuent from fractionator 5:passing via line 7 'direct to extractor 21 in.FIGURE 1 or to extractor61 in FIGURE 2..

The following examples are presented in further illustration of theinvention and ,should not beV construedtoy unduly limit the invention.

In this event the. isoa-mylene feedstock'is fed yto olen,dehydrogenation EXAMPLE I In a process employing the system of FIGURE 1beginning with conduit 19, aqueous methyl carbitol at 100% F. isutilized as the solvent in column 21. The composition of the feedstreamin conduit 19 and various other streams are set forth in Table I interms of pounds per hour.

Table I Stream N o 34 60 39 38 C omponcnt Methane Isouu tene B utene-1Trans-butene Cis-butene-2 Trans-penten C is-pentenc-2 2-rnethylbutene-2Isoprene W atcr Methyl Carbitol 339, 200 864 Total 14, 187 385, 700 8,359 6, 700 67, 000 58, 546 1, 419 5, 791 14, 910

EXAMPLE II In a process employing the system of FIGURE 2 be- 30 tivelyabsorbs said diolen over said monoolen to produce an extract phasecontaining a -substantial portion of said diolen and a small portion ofsaid monoolen in said solvent and a ratlinate phase c-ontaining asubstantial portion of said monoolen, stripping the solvent from saidextract phase to produce an extract concentrated with Table 1l Stream No19 63 62 67 78 75 64 86 Component:

Isobutene 60 Butene 1 2 Trans-bute 2 Cis-butene-2 2 3-methy1butene-1.724 Isopentane. 325 Pentene-l 39 2-methylbutene-1 2, 775 n-Pentane 835Trans-pcntene-2. 108 Cis-pentene-2 54 2-rnethylbutene-2 3, 819 Isoprene161 Methane 235 24, 960 Methyl Alcohol 20, 955 6, 210

Total 33, 471 40, 076

Reasonable variations and modifications are possible within the scope ofthe foregoing disclosure, the drawings and the appended claims to theinvention.

We claim:

1. A process for the separation of a diolen from a rmonoolefn whichcomprises contacting a stream containing said diolefin and saidmonoolefin with liquid methane to produce an extract phase containingliquid methane and said monoolen and a raffinate phase containing saiddiolen.

2. A process in accordance with claim 1 further comprising ashing saidraffinate phase to recover said dioletin as a product of the process.

3. A process in accordance with claim 1 further comprising ashing saidextract phase to obtain a vaporous methane stream and a monoolen productstream, compressing said vaporous methane stream, cooling the thuscompressed vaporous methane stream to produce liquid methane, andrecycling the thus liquefied methane to the step of contacting a streamwith liquid methane.

4. A process in accordance with claim 1 wherein said diolen is isoprene.

respect to said diolefin and recycling the thus recovered solvent tosaid first liquid-liquid extraction zone, introducing said extract intoa second liquid-liquid extraction zone, contacting said extract in saidsecond liquid-liquid extraction Zone with liquid methane to produce asecond extract phase containing liquid methane and a substantial portionof said monoolen and a second ratlinate phase containing said diolene asa highly concentrated product.

7. A process for obtaining a highly concentrated diolen product streamfrom a feedstream comprising a minor amount of said diolen and a majoramount of at least one monoolen, which comprises introducing saidfeedstream into a rst liquid-liquid extraction zone, contacting saidfeedstream in said rst liquid-liquid extraction zone with a solventwhich selectively absorbs said diolen over said monoolen to produce anextract phase containing a major amount of said diolen and a minoramount of said monoolen in said solvent and a raffinate phase containinga substantial portion of said monoolens, stripping the solvent from saidextract phase to produce an extract comprising at least 50 Weightpercent of said diolen and recycling the thus recovered solvent to said7; Afirst liquid-liquid extractionV zone, introducing said extract intoa second liquid-liquid extraction zone, contacting said extract in saidsecond liquid-liquid extraction zone with liquid methane toproduce asecondsextract phase containing liquid methane and a substantial portionof said monoolen and a second ratlinate phase containing p said diolenas a highly concentrated product.

8. vA process in accordance vwith claim 7 wherein saidA diolen is-isoprene and said extract comprises at least` 72 weight percentisoprene.

9. A process for obtaining a highly concentrated iso-` prene productstream from a feedst'ream containing at least one monoolen and less than50 weight percent is0 prene, which comprises introducing said feedstreamintoK a first liquid-liquid extraction zone, contacting said eed- ,Y

stream in said rst liquid-.liquid extractionvzone witha solvent whichselectively absorbs said isoprene overisaid monoolen to produce anextract phase containing said monoolein in said solvent, wherein saidisoprene consti-i tutes at least 72 weight percent of the; extract phaseex=V elusive of said solvent, stripping the solvent from said extractphase to produce an extract containing at least 72 weight percentisoprene .and recycling .the thus'recowy ered solvent tosaidrstliquid-liquid extraction zone, in*y troducing said extract into a secondliquid-liquid extrac. tionzonegcontacting saidextract in said'secondliquid'- liquid extraction zone .with liquid methane Ito produce asecond extract phaseI containing liquid methane and a substantialportion of said monoolen rand a second rafiinate phase containingsaidisoprene in a highly Vconcentrated form.

10. A process in accordance with claim 9 further comt prising separatingmethane from said second extract phaseI and from said second rafnatephaseand recycling theft;

thus recovered methane to said second liquid-liquid extraction Zone.

11; A process in accordance with claim 10 wherein thea,4 methane isArecovered by flashing said second extract phase- 40 the methanecontained ltherein, compressing the resulting;

and b y flashing said second ranate phase,to vaporize;

vaporous methane, condensing the thus compressed vapor-` .j`

ous methane, andV returning the resulting liquid methane` to said secondliquid-liquid extraction Zone.v t

portion of said column to pass downwardly through -said column intocontact with said feedstrearn a solventwhich is immiscible with`liquidmethane, which is selective for said diolen over saidrnonooletinland whichhasasuiciently-low freezing point Ito remain-injthe liquid phase inY contact with `the liquid methane, withdrawingfromsaid column an overhead 'stream comprising'liquidrmethane andmonooleiimgwithdrawing from saidcolumn Aa bottoms stream comprisingsaidysolvent, methane and said diolen, ashingtsaid-bottoms stream torecoverwaporous methane, and fractionating t-he remainder Vof saidbottoms stream to recover a solvent stream and a highly concen-l trateddiolen productstream.y

- 13. process in accordance with claim prising dashing 2said overheadstream to produce vaporous methane,l combining the 'thus producedvaporous Y methane and thevaporous methane produced by lash-Y ing .thesai-d bottoms stream, compressing the-thus cornlbined vaporousmethane-stream, condensing the thus com` pressed .vaporous methane,recyclingY lthe thus producedV liquid methane tovs'aid lower portion yofsaid-colummand recycling .said solvent stream ;to said upper, portion ofsaid column.

14.2A process in accordance `with-.claimV V13 wherein said diolefini isisoprene.

15. "A process inY accordance. :withiclaim V14 whereinV said solvent-ismethyl alcohol.

No references cited.

:DELE-ERT tE. 4kGNLTZ, Primary Examiner.

` G. E; SCHMITKONS, Assistant Examiner.

1. A PROCESS FOR THE SEPARATION OF A DIOLEFIN FROM A MONOOLEFIN WHICHCOMPRISES CONTACTING A STREAM CONTAINING SAID DIOLEFIN AND SAIDMONOOLEFIN WITH LIQUID METHANE TO PRODUCE AN EXTRACT PHASE CONTAININGLIQUID METHANE AND SAID MONOOLEFIN AND A RAFFINATE PHASE CONTAINING SAIDDIOLEFIN.